Mason then signed with the New York Knicks in the summer of 1991. In the 1990–91 season, Mason played 26 games for the CBA's Tulsa Fast Breakers, with whom he averaged 29.9 points and 14.8 rebounds per game in his only season in the league.[1]

Mason won the NBA Sixth Man of the Year award in 1995. He was named to the 1996-'97 All-NBA Third Team and to the NBA All-Defensive Second Team. He led the league in minutes played in 1995-'96 (3,457), also setting a Knicks record with the number. He also led the league in minutes played per game in 1996–97 (43.1).

His first season with the Hornets was the best in his NBA career. He recorded career-highs in minutes played (43.1), points (16.2), rebounds (11.4) and assists (5.7) and also 4 triple-doubles (the first in his career). He missed the entire 1998-'99 season due to a ruptured biceps injury [1], then averaged 11.6 points and 8.5 rebounds the following one.

In Miami, although Mason had been brought over by Miami coach Pat Riley to be a role player on what was thought to have been a contender Heat team, the kidney ailment of Alonzo Mourning forced Mourning to sit out and made Mason a starter for the team. Mason would respond by finishing second on the team in scoring with 16.1 points per game and average 9.6 rebounds. With Mourning and Grant Hill selected but unable to play due to injury in the 2001 NBA All Star Game, Mason was chosen to represent the Heat in his only selection to an All-Star team. Mason helped the Heat make the playoffs with a 50 win season for the injury ravaged Heat. Mason however virtually disappeared in the playoffs, taking only 13 shots and averaging a mere 5.3 points and 3 rebounds in three games. Mason was waived during the offseason.

He signed with the Milwaukee Bucks for the 2001–02 season. In Mason's first season with the Bucks, the team stumbled to a 41-41 record (11 games worse than the previous season) and missed the playoffs altogether. Mason's numbers went down as well: 9.6 ppg, 7.9 rpg. Nonetheless Milwaukee stuck with Mason for another year, waiving him after the 2002–2003 season.

Mason and his former girlfriend are allegedly the subject of the song "I Got a Story to Tell" by The Notorious B.I.G.. In the song, B.I.G. describes a situation in which he was sleeping with another man's girlfriend at that man's house. When the man returns unexpectedly, B.I.G. tied up the girlfriend, then drew a gun on the man and demanded money.[9] He obeyed and B.I.G. left to share this story with his friends. Although B.I.G. never named Mason, he did mention "a player from the New York Knicks" as the girl's boyfriend and that this player's height was 6 feet 5 inches (1.96 m).[9] On May 16, 2016, Fat Joe claimed that "I Got a Story to Tell" was about Mason on the ESPN show Highly Questionable, saying it is a "very strong possibility, rumor" the song is about Mason.[10] Since he died before the reveal, Mason could not comment to confirm whether or not the song is about him.[11] Former teammate John Starks also appeared on Highly Questionable prior to Mason's death in 2015 and was also asked about who "I Got a Story to Tell" was about. Starks said he knew that the events described in the song really happened, but denied to reveal a possible name.[11]